As far as I see from wiki, 'consumer'-grade(non-cryogenic) thermal imaging cameras use microbolometer sensors to get integrated IR intensity over some 5-12um range. But I had an impression, that having just integrated IR intensity you can't get surface temperature precisely, especially with 0.1C precision we see on consumer cameras.

IR thermometers (pyrometers) for example use 2-band IR measurement, but I don't see this principle being used in thermal imaging.

Or there is some sort of 'know-how' matrix of IR band filters in front of the sensor?

From what I know a conventional 'point to shoot' digital camera has an IR filter just before the CCD/CMOS. Removing this and placing a filter opaque to visible light enables you to image using IR. So how is a p2s camera with the IR filter removed any different from a thermal imaging camera?
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Bernhard HeijstekJul 7 '11 at 12:56

I once met a guy who was selling this kind of camera, and I asked him kind of the same question. He said that at these wavelengths, most non-metallic surfaces were very decent black bodies, and thus the integrated irradiance could give a good estimate of the surface temperature. We did not discuss precision though.
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Edgar BonetJul 7 '11 at 14:55

2 Answers
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I'm not an expert at thermography per se, but I've designed and built a commercial microbolometer IR camera and looked at several other cameras (for thermography) and as far as I know, they don't have any "funny business" going on. Commercial handheld thermography cameras require you to input the surface emissivity, air temperature and transmittance parameters etc to get an accurate reading, so obviously in practice for random measurements you won't get anywhere near +/- 1K accuracy, but the noise (precision) can be as low as dozens of mK like quoted.

In industrial (repeatable) applications you can probably calibrate this very accurately though.

Interesting experience :-) Were you using stock sensor for this camera? Have you seen any mosaic filters in these cameras to separate IR bands (although these filter segments might be as small as 17x17um)?
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BarsMonsterJul 7 '11 at 9:49

The sensors are usually very tightly held since they are classified as military equipment in customs regulations etc. I don't think any of them are available "off the shelf". You can buy a "cheap" camera and dismantle it, but you still need the datasheets unless you want to do a fair amount of reverse engineering :). I haven't seen the filters you talk about, is it even possible to do wavelength selectivity of that small size? The wavelength is almost the same order as the required size of the filter...
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BjornWJul 7 '11 at 10:02

I see, you must be right... Filters for 12um range must be quite bulky... Apparently thermal cameras are simpler than I've though :-)
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BarsMonsterJul 7 '11 at 10:26

Regarding the technique of dual filter applications: another local company here manufactured a gas detector camera, which combined two (cooled) IR FPAs to look at the same scene, but put a gas-filled absorption-cell in front of one of them. By some image analysis they could detect gas leakages from oil-rigs etc visually, quite cool. The thermal cameras on the market are not physically rocket-science but have a lot of engineering problems compared to visual cameras.
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BjornWJul 7 '11 at 12:49